Scotty Kilmer is more of an entertainer. He rarely applies a scientific method or thought process to what he recommends. The fact that he mentions "check the air filter" as a fuel savings tip shows which car era he is from (the carbureted one). It simply isn't relevant for modern vehicles. He might "know" some things about vehicle ownership, but he doesn't "understand" how things work.
I generally leave the Prius in normal mode except for rare occasions in the summer when I want the AC to operate more efficiently. There is no discernible difference in fuel economy between the 2 modes. Even worse, eco mode changes the throttle curve to be non-linear. Almost nothing happens for the first 2/3 of the pedal motion, and then it gets extremely twitchy towards the last 1/3 of travel. This actually makes it more difficult to maintain the throttle in the "eco" range of the HSI.
Slow acceleration does not equal improved fuel economy. Most important is brake avoidance. Thankfully Toyota doesn't screw with the brake application curves for the sake of improving fuel economy.
The "eco" button should be repurposed to change the regen behavior. It annoys me that the car regens slightly and slows when letting off the throttle. If I could switch modes so that letting off the throttle enters a pure coast, that would make me happy. Others would be happy to have the car slow at maximum regen when letting off the throttle. That feature is way more valuable to consumers than the awful "Eco" button.
